Photodynamic therapy: a clinical reality in the treatment of cancer.

Photodynamic therapy (PDT) is a minimally invasive treatment with great promise in malignant disease. It can be applied before, or after, chemotherapy, ionising radiation, or surgery, without compromising these treatments or being compromised itself. Unlike radiotherapy and surgery, it can be repeated many times at the same site. Response rates and the durability of response with PDT are as good as, or better than, those with standard locoregional treatments. Furthermore, there is less morbidity and better functional and cosmetic outcome. PDT is valuable for premalignant conditions such as mucosal dysplasia and carcinoma-in-situ. The excellent cosmetic outcome makes it valuable for skin lesions and for lesions of the head, neck, and oral cavity, where another advantage is that it has negligible effects on underlying functional structures. With endoscopic delivery of light to hollow structures, PDT has been successful in the treatment of early gastrointestinal cancers, such as oesophageal cancer, and lung cancer. The superficial effects of PDT can be exploited in the treatment of large areas such as the pleura and peritoneum, where curative radiation doses cannot be tolerated by underlying normal tissue. PDT is an ideal adjuvant therapy when surgical resection of solid tumours might leave behind residual microscopic disease. Interstitial light delivery, where light is fed directly into solid tumours, allows PDT to be used for large, buried tumours that would otherwise require extensive surgical resection.